Offenlegungsschrift DE No. 28 05 691 A1 corresponding to U.S. Pat. No. 4,277,797, discloses a color television receiver with an automatic alignment system containing an alignment computer, a reprogrammable nonvolatile memory, and a screen-image-sensor system with which the screen signals are sensed and fed as actual values to the alignment computer. From the actual values and preset nominal values stored in the memory, the alignment computer derives digital correction signals which give the desired setting of screen parameters, particularly in the horizontal and vertical deflection units. This also replaces the functions otherwise performed in the video-signal-processing unit by setting potentiometers, such as white-level, grey-balance, and beam-current-limiting control.
The U.S. Patent cited above does not deal with the replacement of the setting potentiometer for the focusing voltage. In conventional television receivers, this potentiometer is included in a resistor network which derives the focusing voltage from the high voltage generated for the picture tube, cf., for example, a book by O. Limann, "Fernsehtechnik ohne Ballast", 13th Edition, Munich, 1979, pages 275 to 280. The focusing potentiometer, on the one hand, is usually a high-resistance device (of the order of 10M.OMEGA.) and, on the other hand, must be capable of withstanding high voltages, because it must deliver a voltage on the order of a few kilovolts.